Justify second of tenants getting cross with flat (7)
I believe the answer is:
explain
'justify' is the definition.
(explaining is a kind of justifying)
'second of tenants getting cross with flat' is the wordplay.
'second of tenants' becomes 'e' (lnd letter of 'tenants').
'getting' is a charade indicator (letters next to each other).
'cross' becomes 'x' (X is cross-shaped).
'with' is a charade indicator (letters next to each other).
'flat' becomes 'plain' (I've seen this in other clues).
'e'+'x'+'plain'='EXPLAIN'
(Other definitions for explain that I've seen before include "Show the whys and wherefores" , "Justify" , "Interpret" , "Give reasons for" , "Describe" .)